Gunshot residue (GSR) particles represent the burnt and partially burnt chemical remains of ammunition expelled from a firearm discharge. GSR possesses evidentiary value which can assist investigators in shooting incident reconstruction (Haag, Shooting Incident Reconstruction; Elsevier: Amsterdam, (2006)). Organic GSR (OGSR) is composed primarily of explosive materials originating from the propellant of the discharged ammunition, while inorganic gunshot residue (IGSR) is formed from contributions of the ammunition propellant, primer, projectile (bullet), and cartridge case (Dalby et al., J. Forensic Sci. 55:924 (2010)). Detection of GSR at a crime scene is critical, as it is indicative of a shooting incident. Furthermore, detection of GSR on the body or clothing of a person indicates their presence, and often degree of involvement, in a crime (Cetó et al., Anal. Chem. 84:10306 (2012)).
Recovery, detection, and preservation of these discharge samples is often challenging. Crime scene recovery of GSR can be achieved through several collection methods, including adhesive tapes, glues, liquid swabbing, and vacuum apparatuses (Dalby et al., J. Forensic Sci. 55:924 (2010)). Tape collection, or “tape lifting”, has been established as the most widely accepted and efficient technique for GSR collecting from different surfaces (Degaetano et al., J. Forensic Sci. 35:1087 (1990)). Tape collection is performed by the pressing of double-sided pressure sensitive adhesive (PSA) tape against a surface of interest that contains GSR. These surfaces include the clothing, skin, and hair of a suspect or victim, as well as any surfaces adjacent to the firearm discharge (Romolo et al., Forensic Sci. Int'l 119:195 (2001); Zeichner et al., J. Forensic Sci. 38:571 (1993); Shaffer at al., Scanning 21:99 (1999); Wrobel et al., J. Forensic Sci. 43:178 (1998)).
Scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDS) is the most widely accepted technique for GSR detection (ASTM; American Society for Testing and Materials (2010)). SEM/EDS specializes in the detection of the heavy metals; lead, barium, and antimony, where the presence of all three is considered characteristic to IGSR (Nesbitt et al., J. Forensic Sci. 21:595 (1976)). SEM/EDS analysis has been applied to IGSR detection on several collection substrates. Specialized tape substrates coated with a conductive carbon material are required for SEM analysis. Unfortunately, the collection of debris and fibers from certain surfaces, is known to inhibit SEM analysis of tape collection substrates, as these analytes are not electronically conductive (Mastruko, Forensic Sci. Int'l 136 (Suppl. 1):153 (2003)). Other pitfalls for the technique include relatively expensive instrumentation and time consuming analyses (Romolo et al., Forensic Sci. Int'l 119:195 (2001)). The most rapid SEM/EDS approach was found to take over 8 hours to scan an 12.5 mm2 area for detecting GSR originating from a specific ammunition (Lebiedzik et al., J. Forensic Sci. 45:83 (2000)). A threshold for the number of “characteristic” IGSR particles must be achieved before GSR detection can be confirmed. However, the advent of heavy metal free (HMF) ammunition reduces the probability of detecting “characteristic” IGSR particles and weakens the specificity (rate of true negatives) of the technique for the identification of GSR. GSR particles originating from HMF ammunition are devoid of Pb, Ba, and Sb, and are susceptible to higher rates of misclassification (false negatives, etc.) via SEM/EDS detection (ASTM; American Society for Testing and Materials (2010); Martiny et al., Forensic Sci. Int'l 177:E9 (2008); Garofano et al., Forensic Sci. Int'l 103:1 (1999); Cardinetti et al., Forensic Sci. Int'l 143:1 (2004)). Other elemental analyses, such as laser ablation inductively coupled mass spectrometry (LA-ICPMS), have attempted to reproduce the high-throughput analysis of GSR on tape offered by SEM/EDS (Abrego et al., Anal. Chem. 84:2402 (2012)). Although, LA-ICPMS was reported to be capable of analyzing a 12.8 mm2 area in approximately 66 minutes, it unfortunately required expensive instrumentation and was also dependent upon detection of heavy metals. Additionally, the laser spot diameter of 160 μm provided bulk analysis, eliminating the possibility of detecting individual GSR particles.
Vibrational spectroscopy (IR and Raman) represents an ideal approach for GSR analysis, due to its non-destructive and selective nature. Advanced statistical analysis was used to differentiate Raman spectroscopic data collected from GSR particles originating from different firearm-ammunition combinations (Bueno et al., Anal. Chem. 84:4334. (2012)). Raman spectroscopic analysis of smokeless ammunition propellant and its subsequent GSR was also investigated. Specific chemical additives from the discharged ammunition identified in the resulting GSR, were used as a predictive tool for ammunition identification (López-López et al., Anal. Chem. 84:3581 (2012)). Previous macroscopic ATR-FT-IR investigation into GSR analysis has targeted the differentiation of non-equivalent GSR samples from ATR-FT-IR data (Bueno et al., Anal. Chem. 85:7287 (2013)) and combined Raman spectroscopic and ATR-FT-IR data (Bueno et al., Anal. Methods (2013)). Shooting distance estimations based on GSR analysis were performed via macroscopic ATR-FT-IR analysis (Mou et al., J. of Forensic Sci. 53:1381 (2008)) and traditional FT-IR spectroscopy utilizing KBr pellets (Sharma et al., Science & Justice, 49:197 (2009)). Traditional FT-IR spectroscopy was also previously implemented to characterize organic gunshot residue (OGSR) (Leggett et al., Microchemical Journal 39:76 (1989)). However, these methods have been limited to chemical characterization of GSR.
The present invention is directed to overcoming these and other deficiencies in the art.